Safe and efficient energy storage is a high priority concern today, especially for applications such as electric vehicles and the large scale storage of electric energy to level the load of stationary power plants.
Major improvements in the amount of energy stored per unit weight or volume, at reasonable costs, do not appear to be forthcoming from systems that employ aqueous electrolytes.
Lithium-based battery cells are being pursued currently because lithium is very electropositive and is light in weight. In such lithium-based battery cells, the negative electrode is a lithium alloy, usually aluminum-lithium, the positive electrode is an iron sulfide, and the molten salt electrolyte is a eutectic composition of lithium fluoride, lithium chloride, and lithium bromide. Because of the high melting points of such salts, operation is normally in the temperature range of about 350-500.degree. C.
Electrochemical battery cells using aluminum-lithium negative electrodes are being developed to provide high current and capacity densities, high specific power, and long cycle life. Such cells have application in batteries for powering an electric vehicle or for the storage of electric power generated by electric utilities during periods of off-peak usage. Such electrochemical battery cells using aluminum-lithium negative electrodes also are being developed as replacements for conventional batteries, particularly for applications where high voltage, high capacity, and long shelf life are required. Unlike some conventional batteries, such as nickel cadmium batteries, or even lead acid batteries, which include component materials that may adversely affect the environment, lithium battery cells use component materials which are substantially less harmful.
Although lithium battery cells have numerous advantages over conventional batteries, the high chemical reactivity of lithium has caused problems in the fabrication and safe operation of the cells. For example, lithium is highly reactive with water and if brought into contact with water, will ignite. Lithium also can be unstable when in contact with cell electrolytes. Moreover, after prolonged use, a lithium cell can become unsafe because of the formation of lithium dendrites which can cause shorting within the cell.